In recent years, a chemical reaction performed in water or in an aqueous solution attracts attention because it is superior, in an environmental load, safety and the like, to a reaction performed in an organic solvent, which has been widely performed. Meanwhile, a Lewis acid catalyst is widely applied to Friedel-Crafts alkylation/acylation reactions, various coupling reactions, polycondensation, dislocation, isomerization, dehydration reactions, and the like, and most of these reactions are performed in an organic solvent, and hence, there is a demand for a Lewis acid catalyst which does not decompose but works in water.
A biomass is a renewable resource, and is regarded as a promising novel carbon source to replace crude oil. Above all, glucose is produced from a variety of plant materials, and it is known that 5-hydroxymethylfurfral (HMF) obtained through dehydration of glucose can be a raw material of useful chemical substances such as furfuryl alcohol and tetrahydrofuran. As a reaction for producing HMF from glucose, a method in which glucose is converted into fructose through a hydride transfer reaction, and the fructose is dehydrated to produce HMF is widely employed. In this reaction, a reaction using, as a catalyst, phosphoric acid/TiO2 or phosphoric acid/Nb2O5 is known as a method for producing HMF from a glucose aqueous solution, but such a metal oxide is expensive and hence is industrially difficult to use. Besides, it is reported that Sn-containing β-zeolite is effectively used for producing fructose from a glucose aqueous solution (Non Patent Literature 1). Furthermore, it is reported that HMF can be produced from glucose by using a phosphoric acid compound in which phosphoric acid is incorporated in a skeleton-forming component such as aluminum phosphate (Non Patent Literature 2).